Sometimes it's the little things that make or break your day. When the sheets need changing, is the washer nearby, or down two flights of stairs in a spidery corner of the basement? When nature calls during a crucial part of a favorite television program, can you make a quick bathroom trip?

Case in point: Joe O'Leary's 1,200-square-foot condominium in Chicago's Aqua tower at Lakeshore East has proved every bit as functional as the much larger suburban home he owned previously. O'Leary's two-bedroom, two-bath condo can easily accommodate six dinner guests with its banquette seating, and he has hosted relatives for extended periods without sacrificing much of his privacy.

The secret? A well-executed floor plan that meets his needs. O'Leary's condo has one bedroom and one bath on each side, with an open area in the center for dining and relaxing. A second bedroom has room for a TV and home office, which he uses when no one is visiting.

"It's a one-man place most of the time, but it's comfortable for guests too," he said.

As O'Leary has discovered, a floor plan can make routine tasks easier or a pain. And, in many cases, how space is laid out is just as important, or more important, as how much of it there is.

"Residents don't see a big difference in livability if a unit is 790 square feet instead of 800 square feet," said Sean Linnane, vice president of Magellan Development, which developed O'Leary's building, as well as several other Chicago condo and rental properties. But a tiny difference in square footage for each unit can have a big effect on the overall cost of a project, and in the amount of rent apartment-dwellers pay each month, he said.

Part of Linnane's job includes "scrubbing" the rental units his company builds — developer speak for making sure they are designed as efficiently as possible — while still finding room for walk-in closets, balconies and other sought-after features.

When evaluating or planning a layout, it's crucial to consider the daily habits of the people who'll be living in the space, said Bill Styczynski, president of Downers Grove-based SWA Architects. Does anyone work from home? Where will you store bikes and outdoor equipment? Do you have children or plan to start a family? Will you be the one to host holidays or family gatherings?

The answers to questions such as these help determine which configuration of bedrooms, baths and shared spaces might work best. "Everyone's lifestyle is different," Styczynski said.

Despite their differences, most people end up settling on a floor plan that looks somewhat similar to their neighbor's, said Stuart Cohen, owner of Cohen & Hacker Architecture in Evanston.

"It turns out that almost everybody wants versions of the same thing," he said. "We don't have to reinvent the wheel each time — we just have to customize it." That plan includes a kitchen connecting to a family room, space for shoes and bags near the garage or entry, and a bath for each bedroom, if budget permits.

"Very few people want to come in with a blank sheet of paper," said Brian Brunhofer, president of Meritus Homes. Instead, he said, buyers simply want the flexibility to adapt plans to their preferences and living situations.

Meritus Homes' Made for You program, introduced two years ago, allows buyers to adapt one of the homebuilder's plans to the homesite of the buyer's choice.

Working from established plans allows builders to better predict their costs and time frame for building, Brunhofer said — something that can be comforting to buyers: "We know how to build the plan and what it costs. There's a certain predictability there."

Chicago-based Lexington Homes is another builder that allows buyers to alter floor plans to fit their situation, said Jeff Benach, co-principal of the company. At its Lexington Park town home community in Des Plaines, buyers can forgo a bonus room on the main floor and instead double the size of the kitchen. Another option: more closet space or an expanded master bath, he said.

For most buyers, open floor plans continue to reign supreme, said John Wozniak of Wheaton-based J. Lawrence Homes. At the builder's Remington Landings development in north Aurora, ranch and two-story homes have an open feel in shared living areas, as well as flex rooms that can serve as "study halls" for children's homework or adult media rooms. Prices for the two- to five-bedroom homes start at $260,000.

Flexibility is key

Flexibility is important when creating a floor plan, said Chris Walsh, principal architect of Tandem Architecture and Construction in Lincoln Park, since it is often difficult to envision the twists and turns life takes during the course of homeownership. That's why flex rooms and basements continue to be popular.

"A finished basement can provide the ultimate flex space if you keep it open," Walsh said, with room for guests, large gatherings and, perhaps, a home office.

For most people, seeing a floor plan in three dimensions works best. That's why builders and apartment complexes furnish models for homebuyers to tour.

"Floor plans are an abstraction," Cohen said. "When most people look at them, they just don't have any idea what they are seeing."

If it's not possible to visit the space you are considering, because it's occupied or not yet built, Cohen has a simple fix: Buy a kit at an art supply store that will let you sketch the dimensions, as well as the furniture you plan to place in each room.

RMK Management Corp., which owns and operates 26 rental properties in the Chicago area, has an online tool called Plan Your Space, which allows prospective renters to see how their furnishings might fit into one of the models available at its apartment complexes. Renters can even use a smartphone to access the tool as they are furniture shopping, said Diana Pittro, executive vice president of RMK.

"Someone will say, 'I've got this dining room set from my grandmother,' and it can be difficult to visualize how that will drop into a room," Pittro said. "The tool is particularly helpful for people downsizing or living with a roommate."

To give residents more flexibility with floor plans, The Columbian penthouses on Michigan Avenue have pocket doors that provide connections between living areas when open. When the doors are closed, residents can transform a portion of their unit into a media room, sitting room or an extra...